Integrate mixclient run fix

[danielSanchezQ]

No description provided.

[danielSanchezQ]

Not sure if this need to be just an error or we should actually panic. If the service rely on it 🤔 . At least in the case where we actually return an error:

Ok(Some(stream)) => stream,
Ok(None) => log_error,
Err(e) => panic!

What do you think?

[youngjoon-lee]

In my opinion, it's good to use stream::empty() so that the libp2p backend doesn't need to care about the mixclient mode and just read the stream that will never return something. Actually, I also think it would be okay to make the empty stream returned from the mixclient (instead of making the empty stream in the libp2p backend).

It's also reasonable to treat this as an error. Then, we need a check in the libp2p backend as below:

let stream = ...;   // maybe, empty() ?
if matches!(config.mixnet_client.mode, SenderReceiver(_)) {
  stream = mixnet_client.run();
}

...

loop {
  tokio::select! {
    Some(msg) = stream.next() -> {
      ..
    }
    Some(event) = swarm.next() -> {
      ..
    }
    ..
  }
}

[danielSanchezQ]

Yes, returning an empty stream from the client seems like a cleaner API option.

[youngjoon-lee]

I agree. I'm working on this.

[youngjoon-lee]

6a5e2e9 It took some time to struggle with the compiler :)

I adopted thiserror to avoid the following error when returning either stream::empty() or stream::unfold from mixclient, if the stream type is Stream<Result<_, Box<dyn Error>>>.

error[E0277]: `(dyn StdError + 'static)` cannot be sent between threads safely
  --> mixnet/client/src/config.rs:29:32
   |
29 |             Self::Sender => Ok(stream::empty().boxed()),
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn StdError + 'static)` cannot be sent between threads safely
   |

I think it's good because we are going to use thiserror anyway at some point.

[danielSanchezQ]

You just need to add dyn Error + Send in the code. I think it is better to use thiserror. But I wouldn't like the PR to keep growing too much. We can do that as a refactor later on.

[youngjoon-lee]

Yeah, I agree. I tried to add Send but I faced another error, iirc. I agree with drawing the line here and merge this if it's okay.

[danielSanchezQ]

I think we can go ahead with this @youngjoon-lee

[youngjoon-lee]

yeah, i think so, even though there are something to be improved. i will make issues for them.